1. Field of the Invention
This invention relates to extreme pressure (EP) additives which are added to lubricants to prevent destructive metal-to-metal contact in lubrication of moving surfaces at high pressures and/or temperatures. EP additives are useful in certain gear elements in automotive vehicles and various industrial machines where high pressure can cause a film of lubricant to rupture.
2. Description of the Prior Art
Sulfurized sperm whale oil has been an effective EP agent, but its use has been curtailed by the Endangered Species Act. In search for a substitute, efforts have been made to prepare wax esters chemically similar to those that constitute 70-75% of sperm whale oil. Perlstein et al., JAOCS 51: 35 (1974), describe some synthetic wax ester preparations from fatty compounds, but these were found to be of limited effectiveness.
Sulfurized synthetic lubricant additives have included compounds such as sulfurized polyisobutylene, thienyl derivatives, trithiones, diphenyl disulfide, and di-n-butyl disulfide. Lubricant compositions comprising hydrogen sulfide adducts of olefins are taught in U.S. Pat. No. 2,382,700, 2,468,739, 2,479,996, 3,991,089, and 4,000,078. Polysulfide lubricant additives have also been synthesized, such as the dimethylbenzyl tetrasulfide cutting oil agent taught by Hughes et al. in U.S. Pat. No. 2,790,775. However, none of these compounds have exhibited sufficient extreme pressure values comparable to sulfurized sperm oil.